Pascal's Triangle

Problem Statement

Given numRows, generate the first numRows of Pascal's triangle.

Link to GitHub :Code

For example, given numRows = 5,

Return

Pascal’s Triangle

Pascal’s triangle is a triangular array of the binomial coefficients. Write a function that takes an integer value n as input and prints first n lines of the Pascal’s triangle. Following are the first 6 rows of Pascal’s Triangle.

ex of pascal triangle

[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

Solution

• We need 2 arraylist . One to create arraylist and second to hold all the arraylist
• First arraylist row is used to add initial elements of the array

          row.add(0, 1)
          Note for the first 2 iterations elements would not be altered before adding to allrows

 {1},{1,1}

• J loop iteration would not start till Row Size is greater than one. It is responsible to altering the arrraylist elements so to generate pascal triangle

         {1},{1,1},{1,2,1}

• The contents of the arraylist would be modified based on the size of the array.

public class PascalTriangle {
 
 public static List<List<Integer>> get(int numRows)
 {
  //List to all rows of list
  List<List<Integer>> allRows = new ArrayList<List<Integer>>();
  

  //List to store rows
  List<Integer> row = new ArrayList<Integer>();
  for(int i=0;i<numRows;i++)
  {

    //Row is used to add initial elements of the array
    //Note for the first 2 iterations elements would not be altered before adding 
    //to allrows {1},{1,1}
row.add(0, 1);
   for(int j=1;j<row.size()-1;j++)
    // set j value from the nest element
    row.set(j, row.get(j)+row.get(j+1));
   //Add rows to the arrayList
   allRows.add(new ArrayList<Integer>(row));
  }
  return allRows;
 }

Output

Iteration